[cssom] Specify serialization of <number>

Author: Simon Pieters

cssom/Overview.html

@@ -2599,9 +2599,12 @@ <h4 id="serializing-css-values"><span class="secno">6.6.2 </span>Serializing CSS
  </dd>
 
  <dt>&lt;number&gt;</dt>
- <dd><p class="issue">Browsers seem to use ToString(), but that might give a
- significand which according to some is teh evil (and also currently does
- not parse correctly).</dd>
+ <dd>
+  <p>A base-ten number using digits 0-9 (U+0030 to U+0039) in the shortest form possible, using "<code title="">.</code>" to separate decimals (if any), preceded
+  by "<code title="">-</code>" (U+002D) if it is negative.
+  
+  <p class="note">JavaScript's <code title="">ToString</code> algorithm cannot be used since it can serialize numbers using an exponent, which would not round-trip
+  in CSS.
 
  <dt>&lt;percentage&gt;</dt>
  <dd><p>The &lt;number&gt; component serialized as per &lt;number&gt; followed

cssom/Overview.src.html

@@ -2521,9 +2521,12 @@ <h4>Serializing CSS Values</h4>
  </dd>
 
  <dt>&lt;number></dt>
- <dd><p class="issue">Browsers seem to use ToString(), but that might give a
- significand which according to some is teh evil (and also currently does
- not parse correctly).</p></dd>
+ <dd>
+  <p>A base-ten number using digits 0-9 (U+0030 to U+0039) in the shortest form possible, using "<code title>.</code>" to separate decimals (if any), preceded
+  by "<code title>-</code>" (U+002D) if it is negative.
+  
+  <p class=note>JavaScript's <code title>ToString</code> algorithm cannot be used since it can serialize numbers using an exponent, which would not round-trip
+  in CSS.
 
  <dt>&lt;percentage></dt>
  <dd><p>The &lt;number> component serialized as per &lt;number> followed